1. Field of the Invention
This invention relates to electronic engine control and diagnostics for an internal combustion engine.
2. Prior Art
Internal combustion engines can have a catalyst in the exhaust path to reduce the occurrence of certain gases coming out of the exhaust path. Further, often it is desirable to determine the operating condition of any such catalysts. In certain low emission vehicles there is a light-off catalyst in the exhaust gas stream which must be monitored for hydrocarbon (HC) efficiency. The light off catalyst is a relatively small, quickly acting catalyst typically used in combination with a large, slower acting main catalyst. However, since the light-off catalyst is usually a very small volume catalyst, the efficiency will be low at the high space velocities experienced over most of the time of engine operation. As a result, an onboard diagnostic monitor for catalyst efficiency will be saturated and cannot detect when the light-off catalyst has deteriorated. It would be desirable to be able to determine when such a catalyst has deteriorated.